/Engine/Plugins/Runtime/RigVM/Source/RigVM/Public/RigVMCore/RigVM.h
FormatFunction is an optional argument that allows you to override how operands are displayed, for example, see SRigVMExecutionStackView::PopulateStackView.
[FString](API\Runtime\Core\Containers\FString) GetOperandLabel ( const [FRigVMOperand](API\Plugins\RigVM\RigVMCore\FRigVMOperand) & InOperand, [TFunction](API\Runtime\Core\GenericPlatform\TFunction)< [FString](API\Runtime\Core\Containers\FString)(const [FString](API\Runtime\Core\Containers\FString) &RegisterName, const [FString](API\Runtime\Core\Containers\FString) &RegisterOffsetName)> FormatFunction )